Higher combustion and exhaust temperatures may be exhibited during higher engine loads and/or boosted engine conditions. These higher temperatures may increase nitrogen oxide (NOx) emissions and cause accelerated degradation of catalytic materials in the engine and exhaust system. Exhaust gas recirculation (EGR) is an approach to combat these effects. EGR strategies reduce an oxygen content of intake air by diluting it with exhaust. When the diluted air/exhaust mixture is used in place of ambient air not mixed with exhaust gas to support combustion in the engine, lower combustion and exhaust temperatures are exhibited. EGR also increases fuel economy in gasoline engines by reducing throttling losses and heat rejections.
Alternatively, when engine conditions are not suitable for EGR, one technology for after-treatment of engine exhaust utilizes selective catalytic reduction (SCR) to enable certain chemical reactions to occur between NOx in the exhaust and ammonia (NH3). NH3 is introduced into an engine exhaust system upstream of an SCR catalyst by injecting reductant into an exhaust pathway. The reductant entropically decomposes to NH3 under high temperature conditions. The SCR facilitates the reaction between NH3 and NOx to convert NOx into nitrogen (N2) and water (H2O). However, issues may arise upon injecting reductant into the exhaust pathway. In one example, reductant may be poorly mixed into the exhaust flow (e.g., a first portion of exhaust flow has a higher concentration of urea than a second portion of exhaust flow) which may lead to poor coating of the SCR and poor reactivity between emissions (e.g., NOx) and the SCR.
Thus, exhaust gas mixing, whether with intake air, reductant, or on its own, is vital to achieve optimal engine performance. Attempts to address insufficient exhaust gas mixing include arranging flow mixers along a passage to increase turbulence of gas flowing therethrough.
However, the inventors herein have recognized potential issues with such systems. As one example, these mixers are often complex in design and difficult to incorporate in differently shaped engine systems. For example, the mixers may not accommodate various bends and/or injectors present in a passage. Additionally, molds and/or casts of these mixers are expensive, resulting in increased manufacturing costs.
In one example, the issues described above may be addressed by an engine system comprising a mixing plate arranged between a first passage, a second passage, and an auxiliary passage, each of which is coupled to a chamber, and where the plate is perforated and comprises an S-shaped cross-section separating the chamber into two portions, where the first passage is coupled to a first portion and the second passage is coupled to a second portion. In this way, gas in the first portion (and in one example all of the gas) is forced to flow through the plate before entering the second portion.
As one example, the auxiliary passage is coupled to the first portion. Gases from the first passage and the auxiliary passage may collide in the first portion before flowing through perforations of the plate to the second portion. The plate may increase turbulence which may promote mixing between the gases from the first passage and the auxiliary passage. The mixture may flow through pieces of the second portion before flowing into the second passage. In this way, the mixture may provide increased efficiency and performance in components arranged in the second passage downstream of the plate and chamber.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.